Fatliquoring with tetrakis (hydroxy-alkylene) phosphonium halide and an organic phosphate ester and leather flameproofed thereby



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atent FATLIQUORING WITH TETRAKHS (HYDROXV- ALKYLENE) PHGSPHGNIURI HALIDEAND AN ORGANIC PHOSPHATE ESTER AND LEATHER FLAMEPROOFED THEREBY RichardN. Jones, Reading, Mass, assignor to Swift &

Company, Chicago, 111., a corporation of Illinois N Drawing. Filed Apr.20, 1966, Ser. No. 543,783

11 Claims. (Cl. 8-?423) This invention relates tothe flame-proofing andreduction of afterglow in leathers. The invention is directed to thetreatment of hides and skins with the express purpose of incorporatingself-extinguishing properties into the leather. More specifically, theinvention concerns treatment of mineral tanned leather with certainphosphorus containing compounds and to a unique fat-liquoring processwherein the leather has pronounced resistance to flaming and afterglow.

The military has a definite requirement for pilots gloves which whensubject to flash fires will not ignite and, more important, will notcontinue to have a glowing ash after the actual flame has beenextinguished. Most leathers have a certain resistance to flammability,but mineral tanned leathers do exhibit the afterglow characteristic.Further, glove leather tends to shrink while it is burning resulting inthe fact that the glove must be cut off the pilots hand. The result isthat serious burns to the hands of pilots caught in flash fires hasfrequently occurred. While various workers skilled in the leather arthave been working on the problem over the past -12 years, all efforts toproduce glove leather having dimensional stability and being resistantto afterglow have failed.

The bulk of commercial leathers are tanned with either mineral ions,such as: salts of chromium, zirconium, and aluminum, etc., or organicproducts such as: vegetable tannins, aldehydes, syntans, etc. Organictanning agents do not generally impart the afterglow characteristic toleather, but by the same token, they are often not capable of producingcertain other chemical and physical properties required for many leatherapplications. For example, the requirements for good gloving leather aremore readily satisfied by a mineral tannage since such tannage producesthe soft and stretchy character required for finger dexterity andcomfort, as well as resistance to the harmful effects of perspiration.Yet, on the other hand, mineral tanning agents, especially those ofchromium, often produce in leather a property known as afterglow; thatis, when leather so tanned is subjected to a flame, a slow but steadycombustion of the leather occurs even after the actual flames have beenextinguished. In fact, this steady combustion of the leather resultingin a greenish colored ash is one means of determining Whether a piece ofleather has been chrome tanned.

It is generally necessary to fat-liquor most leathers with fattysubstances of animal, mineral, or vegetable origin to impart the desiredflexibility characteristics as well as other properties to the leather.It is frequently necessary to use these fatty substances to the extentof about /6 to about /3 the dry weight of the leather in order to impartthe desired properties. These fatty substances are combustiblematerials, and it follows that leathers containing moderately highamounts of these fatty substances will be more subject to burning thanif they were absent. Accordingly, it has not been possible tomanufacture a mineral-tanned, heavily fat liquored leather thatexhibited good fire resistance; i.e., resistance to both after-flamingand afterglow.

It is, therefore, an object of this invention to provide leathersegments which exhibit self-extinguishin g propertie and which possesspronounced resistance to afterglow.

It is also an object of the invention to provide a process for treatingmineral-tanned leather which suppresses the tendency of the mineral ionto afterglow as well as imparting the necessary flexibilitycharacteristics to the treated leather.

Additional objects, if not specifically set forth herein, will bereadily apparent to those skilled in the art from the detaileddescription of the invention which follows.

In general, this invention consists of a 2-part treatment that can beapplied to conventionally mineral-tanned leather, retaining all thedesired features which mineraltanning imparts. The first part consistsof retannage with a phosphonium halide to restrict the ability of thechromium ion to afterglow. The second part employs a uniquefat-liquorine composition containing a phosphate ester which aids inrendering the leather resistant to corn bustion. Both steps areimportant. Treatment with only the phosphonium halide will not preventafterglow nor is treatment with only the phosphate ester satisfactory.It is believed that one of the functions of the phosphate ester in thefat-liquoring composition is to curb the combustion of the moreconventional fat-liquoring ingredient. This, in turn, prevents thetemperature of the leather from building u to the point where thephosphonium halide will no longer be effective. The invention is notrestricted to the above theory, however, since this explanation ismerely set forth so that one may better understand the importance ofusing both the phosphonium halide and the phosphate ester. The netresult is a chrome-tanned leather with pronounced resistance to flamingand afterglow. In addition, the leather segments treated in accordancewith the teachings of this invention exhibit improved dimensionalstability when subjected to flame.

At this point, it is mentioned that the words retanned or retannage usedthroughout the specification to classify the treatment of the leatherwith the phosphonium halide should not be given a restrictive meaning.The word retan is used, because, from a sequence of operationsstandpoint, the treatment is applied at the normal point of retanningleather. However, the phosphonium halide treatment does not produce anynoticeable leather effects (added weight, greater roundness, more orless stretch) which are commonly associated with and are generally thesole purpose of conventional retans. Also, it is still possible toinclude conventional retanning steps, if such retannages are deemednecessary to regulate the aforementioned leathering effects.

In the etaiied description which follows, glove leather will be used inthe specific embodiments. However, it should be realized that theprinciples elucidated herein apply to other leathers; that is to saythat while the specific examples in discussion relate to glove leatherthe invention also encompasses the production of fire resistant leathersin general, regardless of their intended use. Further, the term skins asused herein shall include the skins and hides of all animalscommercially tanned, including cattle hide, horsehide, sheepskin,goatskin, pigskin, furs and the like. In addition, the process of theinvention is not restricted to use on mineral-tanned leather. Theprocess may be applied to skins which have been initially tanned by anyof the known methods in commercial practice, although, for reasonsmentioned above, it is most significant in the case of chrome-tannedskins.

In the order of the sequence of events, this invention relates to thetreatment of leather after the normal tanning step. More specifically,after the normal tanning step and the customary mechanical operationswhich follow immediately thereafter (flashing, splitting, shaving, etc.)have been conducted, the skins are ready for treatment with thephosphonium halide and the phosphate ester. The skins are then depositedinto tanning drums and washed. The temperature of the Wash water andthat of the retanning bath may vary widely, up to the shrinkagetemperature of the hide being treated. Generally the skins are washed ata temperature of about 80 F. to 130 F. for to 30 minutes. If theoriginal tannage was completed at a pH below about 4.5, no adjustment inpH is required at this point. On the other hand, if the pH was above4.5, it should be lowered to about 4.0 with a weak acid such as formicor acetic acid. Further, adequate running time for equilibriumconditions to be reached should be contemplated.

After the initial tanning of the skins and adjustment of the pH to belowabout 4.5, preferably in the range of about 3.5 to 4.5, the skins aresubjected to treatment with the phosphonium halide. The desirablehalides utilized in this invention may be best characterized as thosecontaining four hydroxyalkylene radicals directly attached to thephosphorus atoms. Structurally, the phosphonium halide may berepresented by the formula:

wherein x is an integer from 1 to 4 and X is chlorine, bromine, fluorineor iodine. As a practical matter X is usually chlorine or bromine,preferably chlorine as the phosphonium bromide is more expensive thanthe chloride. The amount of phosphonium halide utilized may range fromabout 1l2%, based on the wet, drained weight of the skins. It has beenfound that the best results have been obtained using tetrakis(hydroxymethyl) phosphoriium chloride in an amount between about 0.5% toabout 10.0%, preferably 1.5% to 5%, by weight, based on the weight ofthe drained, tanned skins. Generally, the percentage of the tetrakis(hydroxyalkylene) phosphonium halide employed will depend on the type ofinitial tannage.

Treatment of the skins with tetrakis (hydroxyalkylene) phosphoniumhalide is conducted for a period of time to insure adequate penetrationof the halide: into the skins. This time will vary between minutes and 2hours but will generally be reached in a period of about 30-60 minutes.

To insure reaction of the phosphonium halide with the skin substance, aswell as adequate exhaustion of the halide from the liquor, the leatheris gradually neutralized to a pH of about 6.5 to about 7.5 with a mildalkaline substance such as sodium bicarbonate. This gradualneutralization should take place relatively slowly, i.e., theneutralizing agent should be added in three or four feeds encompassing aperiod of from about 60-90 minutes.

At the completion of this retanning operation, the skins are thoroughlywashed, and the temperature, float, and pH are adjusted as required forthe next step in the operation. This will normally be the drum dyeingprocess, but as previously mentioned, conventional retannages can beincluded at this point if so desired. Said conventional retannages and/or the drum dyeing may be carried out in the usual manner and form nopart of the instant invention.

After this the skins are washed and pH of the system raised to betweenabout 4.0 to 4.5 if the pH at the conclusion of the preceding step wasbelow about 3.5. Washing time and the amount of float will vary, but ithas been found that washing for about 10 minutes at around 120 F. to 130F. is normally adequate.

In the fat-liquoring step, about 4-18% of the fat-liquor composition,based on the weight of the drained, tanned skins is dispersed in about 3to 5 times its weight of water. The liquoring operation is carried outfor a time sulficient to render softness and flexibility characteristicsto the leather. In this connection, the fat-liquor must have a specificexhaust and penetration rate in order to produce the desired results.While time required for liquoring will vary somewhat, it has been foundthat about 30-60 minutes is usually adequate. The skins are then washedfor a short period, say about 5 or 10 minutes at F., and then removedand handled in the usual manner.

The fat-liquors employed may be defined as those conventional sulfatedmono-, diand triglycerides, sulfated fatty acids or any combinationthereof wherein the glyceride or fatty acids contain 8-30 carbons perchain. The glyceride and/or fatty acid can be derived from animal,vegetable or marine sources. The degree of sulfation is important and ithas been found that the degree of sulfation must range between about1.5% to 12% in order to permit a controlled exhaustion rate, and impartto the leather the required temper and surface characteris ticsnecessary for a wide variety of end-use products.

Generally speaking, conventional fat-liquors may be used as long as theyare capable of emulsifying the required amount of phosphate ester. Sincethe skins are treated with about r18%, by Weight, of fat-liquor, andsince the fat-liquor must contain at least 30% phosphate ester, ittherefore follows that at least 1.2% phosphate ester is required forcontacting the skins.

The phosphate esters which are present in at least about 30%, by weight,of the fatty-liquor composition may be defined as alkyl phosphateesters, aryl phosphate esters, alkylaryl phosphate esters and phosphateesters of polyoxyethylenated alkylaryl alcohols or polyoxyethylenatedaliphatic alcohols.

Representatives of the alkyl phosphate esters are the C -C alkyl estersof phosphoric acid. Specific members include trimethyl phosphate,triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentylphosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate,including all isomers as well as mixed esters, i.e., diethyl monobutylphosphate.

Representatives of aryl phosphate esters include all aromatic esters ofphosphoric acid wherein the aromatic portion is unsubstituted orsubstituted with non-interfering groups. Examples are triphenylphosphate and trinaphthyl phosphate. Included within the term alkylarylphosphate esters are the C -C alkyl substituted phenol and naphtholesters of phosphoric acid. Generally the aromatic portion will contain1-3 alkyl groups in ortho, meta, or para positions. A preferred memberof the group is tricresyl phosphate.

The polyoxyethylenated esters may be represented by the formulas:

and

wherein R is selected from the group consisting of (D -C alkyl radicalsand C -C alkyl phenyl radicals, M is a cation and usually an alkalimetal or /2 alkaline earth metal hydrogen or ammonium ion, and n is aninteger of about 1 /2 to about 30. The esters will normally containabout 20-75 percent, by weight, of ethylene oxide. Specific examplesinclude phosphate esters of polyoxyethylenated nonyl phenol containingabout 63% ethylene oxide and phosphate esters of polyoxyethylenatedtridecyl alcohol containing about 52% ethylene oxide.

As a specific, non-limiting embodiment of the invention, one may use afat-liquor composition containing about 5-35 parts of highly sulfatedsperm oil, about 5-35 parts of low sulfated cod plu mineral oil, andabout 30-90 parts of tricresyl phosphate for a combined total of 100parts. The amount in proportion of the 2 sulfated oils is adjusted toproduce the desired exhaustion rate and penetration of the fat-liquor,and will vary depending upon the initial tannage.

At this point, it should be mentioned that tricresyl phosphate, beingwater insoluble, must be emulsified to work in the water system employedin the fat-liquoring step. Several systems were examined, and it wasdiscovered that a proper balance of the materials selected resulted inmore proper stability. This balance required a sulfated oil of combinedS of between about 8% to 12% in conjunction with a sulfated oil ofcombined 80;, of between about 1.5 to 3% in order to produce good gloveleather. The specific combination of oils and emulsifiers to be used ismore related to the properties desired in the leather than it is to thefire retardant properties. That is to say, when glove leather isdesired, the particular fatliquor composition is relatively important ifthe desired finished characteristics are to be obtained.

However, the invention is not restricted to specific fatliquoringcompositions inasmuch as self-extinguishing properties may be renderedto the leather as long as both the phosphonium halide and the phosphateester are utilized. In order to impart the self-extinguishing propertiesas well as the elimination of the afterglow effect to the leather, bothphosphorus containing compounds are required. For example, chrome-tannedcollagen that has been after treated with tetrakis (hydroxymethyl)phosphonium chloride will exhibit fire retardancy but it will possessafterglow and is useless for military gloving purposes unless it isthereafter heavily fat-liquored with the composition containing thephosphate ester. On the other hand, a chrome-tanned leather,fat-liquored with the phosphate ester only exhibits some fire resistancebut also possesses afterglow.

The following examples are presented to illustrate the invention. Itwill be understood that the specific embodiments and illustrationsshould not be taken in any manner as limiting the invention which isdefined in the appended claims.

EXAMPLE I All percentages are based on the pickle weight of the skins.

A quantity of conventionally chrome-tanned sheepskins were placed in atanning drum and washed at 100 F. for about minutes. The pH of thesystem was adjusted to about 4. In a float of 150%, about 1.5% of thetetrakis (hydroxymethyl) phosphonium chloride was added and the systemdrummed for about 30 minutes. The leather was then gradually neutralizedto a pH of about 6.5 to 7.0 with 3% sodium bicarbonate, using 3 feedsduring a period of about 60 minutes to accomplish the neutralization.The leather was then washed for about 5 minutes in a 250% float at atemperature of about 130 F. The skins were then dyed in the usual mannerand after dyeing were washed for about minutes at 120 F. to 130 F. Aquantity of fat-liquor was dispersed in four times its weight of 130 F.water and added to the drum and run for 45 minutes. The quantity offat-liquor utilized was by weight, of the drained tanned skins andconsisted of about 5 4% sulfated sperm oil (8.58.8% S0 content), 5 /4%sulfated cod and mineral oil (2.3-2.5 S0 content) and 4 /2 tricresylphosphate based on the Weight of the skins. The skins were then Washedfor 5 minutes at 100 -F., dumped and allowed to dry. The exhaust of thefat-liquor composition was very good. The temper of the dried leatherwas soft and with run, and the grain surface feel was rich without beinggreasyall of these attributes being necessary requirements of goodgloving leather.

EXAMPLES II-XI Listed below are other examples of the invention whichare typical of the skin types and process variations possible. Each ofthese is like Example I, with the following exceptions:

ALL PERCENTAGES BASED ON THE PICKLE WEIGHT OF SKIN Fat-liquor, percentExample Skin Percent THPC 1 Oil A Oil B Phosphate ester 2 1. 50 3.0 1. 5a 2.00 4.0 7. 5 b 4. 25 2. 0 7. 5 c 3. 00 3. 0 3. 0 d 3. 00 1. 5 1. 5 e

Oil C Oil D VII Calfskin. 1. 5 2. 50 2. 50 5 0 f VIII. Cowhide 3.04.00 1. 50 3. 0 g 5.0 5. 25 5. 25 4. 5 h

7. 5 1.00 3. 00 3.0 i Oowhide 10.0 3.00 0.50 1 5 THPO tetrakis(hydroxymethyl) phosphonium chloride.

Oil A=Sulfated 45 sperm oil (8.5-8.8% S03 content).

Oil B=Sulfated cod and mineral oil (2.3-2.57 S03 content).

Oil C=Sulfated tall oil fatty acid (5.05.2% S03 content).

Oil D=Soap-type containing Oil 0, sheep oil, and soap (32-36% SOrcontent).

2 Phosphate ester: a=triethy1 phosphate, b=tricresyl phosphate,c=tricrosyl phosphate, d=triethyl phosphate, e=triphenyl phosphate,f=tricrosyl phosphate, g=tricresyl phosphate, h=triethyl phosphate,i=tricresyl phosphate, j=triphenyl phosphate.

Leather prepared in accordance with the above Examples was subjected tofire resistant tests. In these tests, rectangular specimen-s of theleather were cut so that they measured 3 inches by 14 inches. Two metalbars of about inch stock measuring 1 by 3 inches were placed on bothsides of the leather specimen along one of its 3 inch edges. Theresulting sandwich was securely tightened in a buret clamp which wasattached to a ring stand so that the grain side of the specimen faceddown. A second ring stand was placed nearby and has fastened to it ahorizontal metal rod. The free end of the leather specimen was drapedover the rod so that the leather was inclined at an angle of 45 with theinclined portion measuring 3 inches by 7 inches. A third metal bar wastaped to the free end to serve as a counterweight. The apparatus wasfurther adjusted so that center of a gas burner was about 2 inches belowthe grain surface and exactly centered underneath the exposed specimen.The gas burner, with air ports closed, was adjusted to produce a flameof about 3 inches in height. The burner was placed in position so thatthe flame played against the specimen for 12 seconds. It was thenquickly removed and the following times noted: (1) afterfiame: timebetween burner removal and cessation of flames on the specimen, i.e.,self-extinguishing properties, and (2) afterglow: period between end ofafterflame and cessation of the reddish afterglow. After the specimencooled, it was removed and the percentage of the original area (21square inches) that was retained was calculated. All leathers testedexhibited less than 5 seconds of afterflame, and less than 10 seconds ofafterglow and hence were deemed to be fire resistant. All leathersexhibited an area retention greater than 50% and hence Were consideredto have good dimension-a1 stability when exposed to flame. All leatherstreated in accordance with the above examples consistently showedexcellent fire resistance and dimensional stability when tested inaccordance with the above method. To the contrary, all other presentlyknown commercial types of gloving leather as well as many other types ofleather, notably those which are chrome-tanned, fail to pass the test.

Obviously many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

I claim:

1. A process for fireproofing skins comprising treating skins withtetrakis (hydroxyalkylene) phosphonium halide and a fat-liquorcomposition containing a phosphate ester whereby the skins becomeresistant to flaming and afterglow.

2. The process of claim 1 wherein the halide is tetrakis (hydroxymethyl)phosphonium chloride.

3. The process of claim 1 wherein the phosphate ester is a memberselected from the group consisting of phosphate esters ofpolyoxyethylenated alkyl aromatic alcohols, phosphate esters ofpolyoxyethylenated aliphatic alcohols, and alkyl, aryl and alkylarylphosphate esters.

4. The process of claim 1 wherein the phosphate ester is tricresylphosphate.

5. The process of claim 1 wherein the halide is tetrakis (hydroxymethyl)phosphonium chloride and is present in an amount of about .5% to 10.0%,based on the drained weight of the skins.

6. The process of claim 1 wherein the halide is tetrakis (hydroxymethyl)phosphonium chloride, the phosphate ester is tricresyl phosphate and thephosphate ester is present in an amount of about 1.2% to 6%, by weight,based on the drained weight of the skins.

7. The process of claim 1 wherein the skins are treated with an aqueoussolution of tetrakis (hydroxymethyl) phosphonium chloride at a pH ofless than about 4.5.

8. The process of claim 1 wherein the phosphonium ester is emulsified ina sulfated glyceride oil having an S0 content of between about 1.5% and12%.

9. The process of claim 8 wherein the sulfated glyceride comprises about5-35 parts of sulfated sperm oil, 5-35 parts of sulfated cod oil and thephosphate ester is tricresyl phosphate.

10. As an article of manufacture, a leather having pronounced resistanceto flaming and afterglow, said leather produced by treating, underacidic conditions, a mineral tanned skin with a tetrakis(hydroxyalkylene) phosphonium halide and a phosphate ester.

11. The article of claim 10' wherein the halide is tetrakis(hydroxymethyl) phosphoniurn chloride and the ester is tricresylphosphate.

References Cited UNITED STATES PATENTS 2,732,278 l/1956 Filachione 894.33 3,104,151 9/1963 Windus 8-94.32 XR NORMAN G. TORCHIN, PrimaryExaminer.

D. LEVY, Assistant Examiner.

U.S. Cl. X.R.

1. A PROCESS FOR FIREPROOFING SKINS COMPRISING TREATING SKINS WITH TETRAKIS (HYDROXYALKYLENE) PHOSPHONIUM HALIDE AND A FAT-LIQUOR COMPOSITION CONTAINING A PHOSPHATE ESTER WHEREBY THE SKINS BECOME RESISTANT TO FLAMING AND "AFTERGLOW." 